Telegraph system



Patented July 4, 1944 Henry M..Bascom, New York, N. Bell Telephone Laboratories,

Y., assignor to Incorporated,

New York, N. Y., a corporation of New York Appiicationiuly 1o, 1943, serial No. 494,211

(c1. iis-es) 6 Claims.

This invention relates toimprovements in telegraph systems and more particularly to improvements in methods and apparatus for the transmission of telegraph signals.

It is frequently desirable to transmit telegraph si'redA to transmit signals from a keyboard transmitter it is necessary to employ a relay toactuate the transfer switch combination because the usual keyboard transmitting arrangement ernployed at the present time is providedA with the equivalent of only a single pair of contacts whicheither close -or open. a single circuit through them. v v

It is an object of .the present invention to transmit signals of different polarity or differenty potential values to atelegraph line yby employing two different sources of electrical` energy and controlling these sources under the control of transmitting apparatus. which merely opens or closes a single circuit through the transmitting` device in accordance with the signalstobe transmitted.

Transmitting arrangements of asimilar type,

have been proposed in the past for certain types of transmission. In the arrangements-proposed in the past theimpedance through the transmitting device is diiferent during vthe transmission of the different signaling conditions. However, when it' is attempted to employ this. type of transmission in combination with the transmitting system disclosed'in United States patents granted tov Cramer 2,131,870, on October 4, 19.38, and 2,1431000granted on January 10, 1939, in which variations in leakage resistance of the line do not change nor'alter the characteristicsy or distortion of telegraph signals the differencel in impedance presented to the line during the two signalingconditions causes considerable distortion. Consequently, a sending arrangementof these typesgintroducesacertain amountof distortion', yfrequently called bias, ,to the telegraph signals and thus partially'nullies the advantage of the-typeof'transmission vdescribed in the aboveidentified patents and in general tends to transmit A'inferior telegraph vsignals in any: type of transmissionY system;

Another object of the present inventionis to provide an arrangement for. overcoming thisdisadvantage by insuring that the impedanceY and transmitting apparatusv connected to the line isi substantially'the same for allsignaling condi.- tions applied to the line.

In accordancezwith this invention a non-linear impedance element is inserted inseries with the transmission circuit or line circuithin such a way that the impedance ofthe non-linear element varies with the signalingcondition in aV manner opposite to themannerof variation of the transmitting circuit and apparatus.

yInthe embodiment of the invention .shown in the drawing the variations in impedance presented to the line by telegraph transmitting systems which employ transmitting apparatus which only opens and Ycloses the line andA at the same timetransmits different polarities to the line is compensated for by connectingaunilateral conducting device'in parallel with a resistance and connecting the parallely combination in series with the line. The unilateral conductling ldevice and resistance combination are arranged so that they will have one impedance when current flows Athrough them in one direction and a different impedance whenV current iiows through them in the opposite direction.` In this manner it is possible to insure that the r,combined impedance of the transmitting lapparatus and this network provide the same'valueof impedance between the line and, ground during thev application of all of the the line.

The foregoing objects and features of the invention, the novel features of Which. are specically set forth intheV claims appended hereto, may be more-readily understood from the following description of a ,specific embodiment thereof when, read with reference to the drawing which shows yin detail one manner of incorporating the invention ina telegraphi'system.

Inl the specic embodiment of the invention described hereinthe invention has been applied signalingconditions to to the subscribers station of the transniittingar-V rangement described in the above-identied patent to Cramer 2,143,000 in which variations, of the leakage resistance of the line. do -notv alter. nor change the bias of telegraph signals usually 1 encountered in telegraph transmission systems. The drawing included'herewith shows4 the details of the subscribers Vstation which 'may be .sub-

stitutedV for the subscribers station `shownin,

Fig. 1 of said above-identified patent. There'i'illimenty at the distant terminating 'oice issymbolically represented. by box I3. This equipmentv contacts I8. Thus relay |5 repeats received signals to the selector magnet |'I of the printing or receiving portion of telegraph equipment I6 at the subscribers station in the well-known manner described in the `.above-identified patents to Cramer.

As pointed out in the above-identiiied Patent 2,143,000 granted to Cramer, it is necessary to apply equal and opposite voltages to conductor |4 extending to the distant terminal of line I4 in accordance with the signals to be transmitted over this line in order to secure the freedom from tant end which causes the ringer to be actul ated to call the subscriber. K

The subscriber either in initiating a call or answering a call will actuate switch I to its operated position where the circuit of the ringer is interrupted and a number of other circuits completed. The lowermost contacts of switch I0 complete the circuit through battery 2| while the second set of contacts from the bottom complete the circuit through battery 20 to the line circuit as will be described hereinafter. The next two sets of contacts, namely the second and third set of contacts from the top of switch I0, apply power to motor I9 of the printing telegraph equipment I6 at the subscribers station.

The telegraph equipment I6 may be of any suitable type and generally will include a group of transmitting contacts I8, preferably actuated by a keyboard, and a receiving instrument or device controlled by receiving or selector magnet |'I. In the embodiment of this invention shown in the drawing the telegraph equipmentJ I6 comprises a printing telegraph transmitting and receiving device, typical examples of which are described in United States Patent 1,745,633, granted to S. Morton et al. on February 4, 1930, and 1,904,164 also granted to S. Morton et al. on April 18, 1933.

The top contacts of switch I U complete the line circuit from line I4 to the upper winding of receiving relay I5, the noise suppression network or inductance 26, resistance 24 and unilateral conducting device or rectier 23 in parallel, battery 2|, and lower operated contacts of switch I0 to ground through the closed contacts of the transmitting device 8.

The `transmitting contacts I8 merely opens and closes the circuit in accordance with the signals to be transmitted from the keyboard in the manner described in greater detail in the aboveidentied patents to Morton et al.

Receiving relay I is also provided with a lower or biasing winding the circuit of which extends from battery through the second set of contacts from the bottom of the operated switch I0, resistance 2'I, and lower winding of relay I5 to ground. As described in the above-identied patents to Cramer, current flowing through the lower winding of relay I5 tends to maintain this relay in the position shown in the drawing. When spacing signals are received over the line the current flowing through the upper winding of relay overcomes the effect of current flowing through the lower winding of this relay and causes the. relay to be operated to its right-hand position where it interrupts the circuit through the selector printing magnet |'I of the receiving equipment I6. 'The circuit for the selector magnet at this time extends from ground through the contacts of relay I5, the network 22 comprising a condenser and another unilateral conducting device or rectifier, winding of magnet I'I, battery 2|,A

the lower contacts of switch l0 to ground through distortion of the telegraph signals. It is also Y necessary that the impedance from line I4 to ground should be substantially the same during the application of both of these potentials to the line. If the impedance and the effective voltage tends through switch station are not substantially the same during the application of both signaling conditions to the line the cable capacity of line I4 will be charged and discharged at different rates during the application of the different signaling conditions to the line and thus tend to distort the telegraph i signals. However, when the impedance and effective voltage between the line and ground are the same under both conditions the charging and discharging time of the line will be substantially the same under both conditions and hence no distortion of the type frequently called bias distortion is caused by the transmitting equipment.

Furthermore, as pointed out above, due to the fact that the transmitting device I8 merely opens and closes the circuit through it in accordance with the signals to be transmitted it has been necessary in the past to provide at least one and in the patent to Cramer, two repeating relays to apply the opposite voltages to the line. In accordance with the present invention the necessity for the one or two repeating relays to apply the two voltages to the line has been eliminated.

When it is desired to transmit from the subscribers station over line I4 the transmitting device is actuated. This device in turn causes contacts I8 to open-and close the circuit through them in accordance with the signals transmitted over the line. As shown in the drawing, the positive terminal of battery 2| is connected to ground through the transmitting contacts I8 while the negative terminal of this battery is connected through the network comprising rectifier 23 and resistance 24, the network 26 and upper winding'of relay I5 tov line I4 through switch I0. `When contacts open, the line circuit then eX- jl, the upper winding of relay I5, network 26, the network comprising the unilateral conducting device 23 and resistance 24 in parallel, battery 2|, lower contacts of switch I0, resistance 25, second set of contacts from the bottom of switch I0 to the positive terminal of battery 20. v o

`Battery y2|) is thus connected in opposition to battery 2|. Battery 20' is designed to supply twicethe potential of, battery 65.50 that the voltage actually applied vto the line will be equal to the voltage of battery 65 but opposite in polarity. Thus, assume;v for example, that battery 2| develops65 volts sorthat la negative voltage of ,65 voltsis applied to the line I4 when contacts I8 are closed'. Then battery 2| should develop, volts which in turn ,will apply |-65 v olts'to line I4 when contacts |8ar`e open. However, under these circumstances the line circuit extends through resistance 25 in addition vto batteries 2| and 20. WhenA n contacts I8 are yclosed the line circuit extends directly through finission -offfsignalsvby the'-transmittingfcontacts vthese contacts to ground and not through re'- sistance 25. It should be noted that when contacts I8 are :closedfresistor 25Sis connected di- -rectly across the highvoltage battery so that the resistance of resistor must be of considerable magnitude.

' Consequently, when contacts I8 are open the additional impedance of resistance 25 is connected in series with line I4 which impedance is-Ynotfconnected Iin series with the line when contacts I8 are closed. Hence thev impedance rfrom the line to ground is different when contacts I8 are open and when they lare closed. -The diierence of impedance will tend to distort the telegraph signals in the manner described above.

In order tov compensate for the Variation in impedance from the line to ground when contacts IS are opened and closed, a network com'- prising the unilateral conducting device which, in the preferred embodiment of vthe invention may be a rectiier 23, is connected in parallel with resistance 25 and the parallel combination connected in series between battery 2| and the noise suppression network 26. Therectier is so connected in the line that it has a very high impedance during the time contacts I8 are closed. In other words, it prevents the flow o current due to the application of a negative potential to the line by battery 2l during lthe time contacts I8 are closed. This means that the line current must ilow through the additional resistance 2d during the time contacts I8 are closed. However the line current will reverse due to the reversal of the Voltage applied to the line when contacts rectier or the unilateral conducting device 23 is so arranged that it will present practically a short-circuit around resistance 24 at this time. In this manner resistance 24 is, in effect, automatically inserted in the line circuit when contacts I8 are closed and automatically removed from the line when contacts I8 are opened. It is thus apparent that resistance 24 is, in effect, inserted in series with the line when resistance 25 is removed from the line while resistance 24 is removed from the line when resistance 25 is inserted in the line. By suitably choosing resistances 2B and 25 and the rectifier element 23 and making the voltage of battery 20 equal to twice that of battery 2| it is possible to have the impedance and effective voltage from the line to ground when contacts I3 are closed substantially the same as when contacts I8 .are opened. W hen these conditions are fulfilled the transmitting equipment willnot cause bias distortion of the telegraph signals transmitted from the transmitting contacts I8 so that the full benefits of the type of transmission described in the above-identified Cramer patents may be obtained and at the same time without necessity of the repeating relays for transmission from the subscribers station. The elimination of these relays materially reduces the amount of maintenance and sources of troubles and errors in the transmission from the subscribers station.

As described in the above-identified Cramer Patent 2,143,000, the selector magnet I1 also follows the signals transmitted by the transmitting contacts I8. Inasmuch as the polarity at the upper terminal of battery 2l is reversed, as described above, in accordance with the trans- I8 are opened. The

selector' magnetl I1 when the transmittingfcon'- tac-ts' I8 are closed but presents a highf'impedance to the current flowing through the circuit -of magnet I'I WhencOntacts-IS are opened. This,

in eiect, causes magnet 'I'I to receive current during the time contacts I8 are closed andfno current during the time these contacts are opened. In this manner magnet I'I receives and follows V'the signals transmitted to line lIll by contacts I8. f

The additional'current taken by magnet I'I during the'time contacts I8 are closed may, in eiect, cause a minor variation in the effective resistance between conductor IiljandI 'ground 'during the' timefcontacts Iii-are opened and "closed, "Hoyt/ever; ,this small variation may be compensated fori by a small diierencein the impedance of lthe rectiver 23 andresistances `v24, and 25 so that the effective impedance between line Illk and ground,"A includingthe impedance of selector magnet IIanzd rectifier 22 as welljas the other impedances discussed above, will b e substantially the same both during the time contactsv i8' are closed and during the time con#l 'tacts' I8 are opened. j

vAt the completion of transmission to or from thesubscribers station -shown in vthe drawing, switch I0 will be restored to "the'position shown in the drawing whereupon the circuits assume their idle condition and then await the reclosing of switch I0 to initiate the next transmission to or from this station.

What is claimed is:

1. In a'telegraph system, a telegraph transmission conductor, telegraph signal transmitting apparatus capable of opening and closing a single circuit only, two sources of electrical energy, electrical connections including impedance elements connected between said conductor and said transmitting apparatus and said sources of energy for transmitting two different signaling conditions to said conductor, and a non-linear impedance element connected in said conductor to maintain the combined impedance of said nonlinear element and said connections and said transmitting device substantially constant.

2. In a telegraph system, a signal transmission conductor, telegraph transmitting apparatus capable of opening and closing only a single circuit in accordance with telegraph signals to be transmitted, an impedance element, two sources of electrical energy, circuit connections for connecting said impedance element and said two sources of electrical energy in series relation with each other and with said conductor, circuit connections for including said impedance element and one of said sources of energy in said single .circuit of said transmitting apparatus, a nonrst source connected in series with said path in opposition to said rst source of electrical energy, telegraph transmitting apparatus connected in shunt relation to saidpimpedance and one of said sources of energy for completing a shunt around said impedance and source of energy in accordance with signals to be transmitted, and a unilateral conducting circuit element also connected in said series circuit for maintaining the impedance of said series circuit substantially constant independently of the completion of said shunt.

4. In combination, a transmission conductor, an impedance element connected in series with said conductor, a rst source of electrical energy connected in series with said conductor, a second source of electrical energy having a magnitude of substantially twice the magnitude of said rst source and also connected in series with said conductor in opposition to said first source,

transmitting apparatus for shunting said impedance and said second source in accordance with signals to be transmitted over said conductor, and a unilateral conducting device connected to said conductor to maintain the impedance of said series circuit substantially constant independently of said shunting of said impedance.

5. In a telegraph transmission system in which the distortion of received signals is independent of variations of leakage resistance, a transmission conductor, means for applying two substantially equal and opposite voltages to one end of said conductor comprising a rst source of voltage connected in series circuit relation with said conductor, a second source of voltage of substantially twice the magnitude of said ilrst source connected in a series circuit relation with said rst source and said conductor and in opposition to said rst source, an impedance element connected in series relation with said second source, a, shunt circuit connected around said impedance and said second source, telegraph transmitting apparatus connected in said shunt circuit for opening and closing said shunt circuit in accordance with signals to be transmitted, and a network connected in series with one end of said line, a unilateral conducting device for maintaining the impedance of said series circuit from said line substantially constant independently of the opening and closing of said shunt circuit.

6. In a telegraph system, a telegraph trans- `mission channel, a plurality of sources of potential, a transmitting apparatus for transmitting the signals -capable of only opening and closing a single circuit in accordance With signals transmitted, connections between said transmitting apparatus and said channel and said sources of potential for causing two different polarities of potential to be connected to said line in accordance with the opening and closing of said single circuit by said transmitting device, and a network comprising a unilateral conducting device included in said connections for maintaining the impedance through said circuit and transmitting apparatus substantially the same when each of said polarities is applied to said line.

HENRY M. BASCOM. 

